Scoping

Scoping is an important part of language definition. Most language workbenches focus primarily on syntax. Mechanisms for specifying static and dynamic semantics — including scoping — are still experimental or limited. Freon is one of the first workbenches to offer a meta-language for declaratively defining scoping rules.

The way Freon handles scoping is based on scope graph theory, developed at Delft University by Eelco Visser and colleagues (see, for instance, https://pl.ewi.tudelft.nl/research/projects/scope-graphs/). Spoofax, a workbench created at Delft University, also provides a meta-language for scoping. While both are inspired by the same ideas, they use different terminology.

To explain Freon’s scoper definition, we first need some common ground about scoping and the concepts used to describe it. The final page of this section will demonstrate how to write a Freon scoper definition.

Running the Scoper Generator

The scope provider definition, written in the Freon meta-language, serves as input for the scoper generator. The generated scoper is then used in the Freon editor. The generator runs automatically with the freon all command is executed, but can also be executed independently using:

npm run freon scope-it -d src/defs -o src/

Incomplete code

It is best to start with the all command. After that, it’s safe to run individual commands.

The individual commands produce code that may be incomplete. For example, the scoper and validator may depend on the typer and attempt to reference its class, which might not yet be generated. Similarly, the editor may try to include the scoper.